Three-dimensional (3D) printed parts result in a physical object being fabricated from a 3D digital image by laying down consecutive thin layers of material.
Typically these 3D printed parts can be made by a variety of means, such as selective laser melting or sintering, which operate by having a powder bed onto which an energy beam is projected to melt the top layer of the powder bed so that it welds onto a substrate or a substratum. This melting process is repeated to add additional layers to the substratum to incrementally build up the part until completely fabricated.
These printing methods are significantly time consuming to perform and it may take several days, or weeks, to fabricate a reasonable sized object. The problem is compounded for complex objects comprising intricate component parts. This substantially reduces the utility of 3D printers and is one of the key barriers currently impeding large-scale adoption of 3D printing by consumers and in industry.
Power is also a significant limiting factor for existing 3D printing methods and devices.
Whilst selective electron beam melting can be used as a powerful material fabrication method, this must typically be performed in a vacuum because interaction between charged particle beams and air molecules at atmospheric pressure causes dispersion and attenuation of the beams, significantly impairing their power. It is, therefore, known to use an assembly comprising a high-powered electron gun (for example, a 150 kW electron gun) contained inside a first vacuum housing that is adjoined to a second vacuum housing containing a workpiece to be operated on. Such assemblies, however, result in low productivity rates due to the required pumping time for evacuating the housings. The practical size of the workpiece that may be contained inside the second housing is also substantially limited.
It is, therefore, also known to use a plasma window in conjunction with a high-powered electron gun to perform material fabrication work. Such an assembly comprises an electron gun contained in a vacuum chamber, wherein the vacuum chamber is adjoined to a region of higher pressure (such as atmospheric pressure) containing a workpiece. A beam of charged particles is discharged from within the vacuum chamber and out of the chamber via a beam exit disposed in a wall of the chamber.
A plasma interface is disposed at the beam exit comprising an elongate channel for bonding a plasma. A plasma-forming gas, such as helium, argon or nitrogen, that is highly ionized, is injected into the channel. Electrical currents are applied to a cathode and an anode disposed at opposite ends of the channel which causes a plasma to form and bond statically between the cathode and anode. The plasma serves to prevent pressure communication between the higher pressure region and the vacuum chamber whilst permitting substantially unhindered propagation of charged particles from the vacuum chamber to the higher pressure region, via the channel, and onto the workpiece.
Whilst plasma interfaces constructed in the above manner also serve to pump down the vacuum chamber, this pumping action is weak and of limited effectiveness only. In practice, both the vacuum chamber and the plasma interface's channel must be pumped such that they are substantially in vacuum prior to the formation of the plasma. This is time consuming and, to implement effectively, requires equipment that is costly and mechanically cumbersome. Particle gun assemblies that comprise plasma interfaces constructed in this manner are, therefore, not well suited for 3D printing apparatuses, where the gun assembly is required to be dexterous and flexible in operation.